The phrase “primary nozzle” is selected herein to indicate a nozzle used to achieve or help achieve flame collapse. Primary nozzles throw large gpm's of foam. A primary nozzle creates a primary stream. In the footprint system, primary streams are generally applied to a tank parallel.
Absent unusual circumstances, in the footprint system primary nozzle(s) is/are staged “upwind” of a tank to create stream(s) generally aligned with the wind. If the surface of a tank is viewed as a clock, the location vis-a vis the tank where the primary nozzle(s) is/are staged, again which is usually upwind of the tank, is helpfully referred to as the six o'clock position. The general direction across the tank from where the primary nozzle(s) is/are staged, again usually the down wind position, is then referred to as the twelve o'clock position. The three o'clock and the nine o'clock positions follow therefrom.
Streams defined by primary nozzles need not rigorously parallel the wind direction and each other; however, in the footprint system their streams would usually not define an angle more than plus or minus 45° with the wind direction or with each other.
The phrase “flame collapse” is used herein to indicate a laying down of at least 50% of the flame. The phrase “preferred flame collapse” is used to indicate a laying down of at least 80% of the flame. Flame collapse in industrial tank fires is typically achieved by blanketing at least a substantial surface area of a tank with foam.
It has been discovered in large tanks, such as tanks of 200-foot diameter or greater, that flame collapse (and preferred flame collapse) can usually be achieved by staging one or more primary nozzles such that they create adequate footprint(s) of foam on the tank surface such that the foam “run” blankets the surface. Subsequent to flame collapse (and/or preferred flame collapse,) however, a “smiley face” frequently remains. The phrase “smiley face” refers to a condition in the tank where flames remain, after initial flame collapse, proximate to inner wall portions closest to the staging area, or generally in the four o'clock to eight o'clock position.